The long-term goal of this research is the biochemical understanding of the transport of beta-carotene from serum to milk and the regulation of this process. This project will be conducted in two phases. As detailed quantitative information about retinoids and carotenoids in human milk is lacking, our objective in Phase I is to identify the major carotenoids and retinoids in pooled samples of mature milk and colostrum. Diurnal variation of beta-carotene and retinal will be determined in mature milk samples. In addition, as the relationship of milk carotenoids and retinoids with serum levels, dietary intake and/or adipose stores is not known, we will also identify and quantitate the major carotenoids and retinoids in pooled samples of these tissues from the same individuals. Dietary intake will be assessed through a combined diet history/diet record approach. In Phase II of the project, by supplementing normal (US) vs. deficient (Guatemalan) mothers with beta-carotene, we will trace the kinetics of transfer of dietary beta-carotene to serum, adipose tissue and/or milk and infant serum. As beta-carotene may be metabolized to retinol, particularly in deficient mothers, retinol (and/or retinylesters) will also be monitored in this study. As before. the relationship to serum, adipose stores and dietary intake will be studied. As vitamin A-deficient children, and in particular breastfed infants, are at increased risk for death due to respiratory and gastrointestinal disease, the results of these studies will have significant practical application to child health.